We are currently solving the structure of Fragment D from human fibrinogen. The primary function of human fibrinogen is to prevent blood loss. This is accomplished when thrombin acts on fibrinogen to form fibrin, an insoluble polymeric network which can trap red blood cells and prevent further plasma loss. Fragment D is the major proteolytic fragment of digested fibrinogen which contains the "holes" part of the "knob-holes" involved in polymerization. We're presently collecting data on several potential derivatives and hope that rapid data collection and high flux synchrotron radiation will improve our resolution.